An interest in water-borne coatings and printing formulations has been increased by regulatory and environmental concerns. In order to reduce or eliminate organic solvents from formulations, the solvents used should be replaced partially or completely with water from coating formulations to obtain the low volatile organic carbon (VOC) content. The possible methods of eliminating or minimizing organic solvents in coating and printing formulations include the following:
1. The coating and printing systems employ a polymer solution as a binder in a mixed organic and aqueous solvent. This method only partially eliminates the need for organic solvents. PA0 2. The coatings and printing ink systems employ an aqueous polymer solution as a binder. This method is limited to water-soluble polymers and fails to provide water-resistance to the finished products. In addition, a large amount of water needs to be removed, which limits its use in some applications such as printing where the printing press speed must be reduced due to slow drying of inks on substrates. PA0 3. The coating and printing systems employ an aqueous solution of alkali salts (e.g., sodium, potassium, ammonium, etc.) of polymers used as a binder. Acrylic-based polymers are widely used in formulating water-based inks and coatings. If ammonium salt of acrylic polymer is used, the change in pH of the product due to escape of ammonia creates several problems in the printing process as well affects end-use properties of the coatings and printing films. PA0 4. The printing and coating systems employ a blend of the polymers as a binder. In general, the properties of printed ink/coating films are significantly improved as compared to a system without the polymer blends. PA0 (A) contacting substantially dry acrylic polymer with a solubilizing amount of an alkaline solution comprising an amine or ammonium compound dissolved in water so as to achieve an acrylic polymer solution having a pH of at least about 10, PA0 (B) heating the acrylic polymer solution formed by step (A) at a sufficient temperature to result in an acrylic polymer solution having a pH of less than about 9, PA0 (C) contacting the acrylic polymer solution formed by step (B) with a water dispersible polyester material having carbonyloxy linking groups in the linear molecular structure wherein up to 80% of the linking groups may be carboxylamido linking groups, the polymer having an inherent viscosity of from about 0.1 to about 0.5 measured in a 60/40 parts by weight solution of phenol/tetrachloroethane at 25.degree. C. and at a concentration of 0.25 grams of polymer in 100 mL of the solvent, the polymer containing substantially equimolar proportions of acid equivalents (100 mol %) to hydroxy and amino equivalents (100 mol %), the polymer comprising the reaction products of (a), (b), (c) and (d) from the following components or ester forming or esteramide forming derivatives thereof: PA0 said contacting occurring under agitation and at a sufficient temperature of about 80.degree. C. to about 99.degree. C. to result in a polymer blend wherein the polyester is substantially completely dispersed in the acrylic polymer solution, and the weight ratio of acrylic polymer:polyester is about 1:99 to about 50:50, PA0 (D) cooling the polymer blend composition of step (C) to a temperature range of about 45.degree. C. to less than about 80.degree. C., wherein a C.sub.1 -C.sub.4 alcohol or a mixture of a C.sub.1 -C.sub.4 alcohol and propylene glycol is added at a concentration of about 2 to about 10% of the ultimate total polymer blend composition, PA0 (E) further cooling the polymer blend composition of step (C) to less than about 45.degree. C., PA0 ln=natural logarithm; PA0 t.sub.s =sample flow time; PA0 t.sub.o =solvent-blank flow time; and PA0 C=concentration of polymer in grams per 100 mL of solvent=0.25.
U.S. Pat. Nos. 4,704,309, 4,738,785, 4,883,714 and 4,847,316 relate to an aqueous ink composition containing water-dispersible polyester. The aqueous inks containing such a polymeric material have many desirable properties such as good adhesion to a variety of substrates and a wide viscosity range. However, despite the advantages obtained using such a polymeric material in aqueous inks, it is known that aqueous inks with such a polymer by itself have been alleged to have problems like poor water resistance and poor block resistance on certain substrates.
U.S. Pat. No. 4,623,680 teaches a method of preparing polymer blends from ammonium or amine salt of a carboxyl functional acrylic copolymer mixed with phenolplast resins useful as can coating compositions. The polyepoxide resins partially reacted with a monofunctional acid group and, optionally, an epoxidized hydrocarbon or vegetable oil.
U.S. Pat. No. 4,395,500 by Gernot et al. discloses a method of preparing polymer blend of styrene and esters of acrylic or methacrylic acid. The aqueous resin solution provides a bimodel particle size distribution with 10 weight % of particles having an average diameter of less than 0.2 .mu.m and of 90 weight % of particles having an average diameter of more than 0.25 .mu.m. The ratio of average grain size of coarse to fine polymer is at least 2:1.
These resin dispersions are claimed to be suitable especially as binder in plasters and gloss paints.
U.S. Pat. No. 4,921,899 discloses an ink composition containing a blend of a polyester, an acrylic polymer and a vinyl polymer. The water-based inks containing the blend of these polymers as a binder are taught to be able to significantly improve ink film properties such as alcohol resistance, block resistance and water resistance as compared to water-dispersible polyester alone. The polymer blends were also employed to prepare ink primers and overprint varnishes. However, these polymer blends were prepared by mixing an aqueous polyester dispersion with an acrylic emulsion which contains surfactants and other additives. The presence of surfactants in the ink formulations creates several problems related to ink stability, printing process and print quality of the ink film.
U.S. patent application No. 225,520 relates to an ink composition containing a blend of a polyester and an acrylic polymer. It was observed that the water-dispersible polyester material, when mixed with an acrylic polymer, can provide good water resistance and good block resistance without sacrifice of the advantages of water-dispersible polyester alone. This polymer blend was used to formulate water-based inks, overprints, and ink primers. As with U.S. Pat. No. 4,921,899, the polyester/acrylic blends were prepared by mixing polyester dispersions with acrylic emulsions containing surfactants and other additives.
In order to avoid prior art problems and uncertainty of ink performance, it would be desirable to have a process for preparing water dispersible blends of polyesters and acrylic polymer that avoids the need for surfactants.